Diaz: You, I heard you are going to have a wedding after this battle. There is no guarantee of coming back alive.
Zieg: Even if one of us dies, our bonds of affection are forever.
Diaz: Your eyes are already looking at our future! Then I will realize it for you! Disc 3: Flashback at Fort Magrad
Recognized by the Red-Eye Dragoon Spirit, Zieg was one of the heroes of the Dragon Campaign and Rose's betrothed. 11,000 years ago, she witnessed his sword pierce Melbu Frahma, bringing victory to the Humans, but his final moments as the spell of petrification claimed his body would forever be etched into her mind.
11,000 years later, it is still with regret that Rose recalls the memory and sensation of having let go of his hand as Vellweb crumbled, even though his last wish was for her to save herself:
Zieg... If my hands could grab him, I wouldn't have had this bitterness.
Most moments between Zieg and Rose are told in flashbacks that Rose has in the later half of the game, and scattered mentions here and there. Zieg is first introduced to the player as part of Rose's memory in the Dragon Campaign FMV on disc 2, though he doesn't reveal himself to the party as the villain they've been fighting before the end of disc 3, which is when the player realizes that Dart has been talking about him all along – not by name, but as his father. During the festivities at the end of disc 2, Rose thinks of him when she is by herself ("[I am... a hero... He would laugh at me...]", she says in response to the nation of Tiberoa celebrating the group, which makes her chuckle). It is Zieg who was at Rose's side when she became the Darkness Dragoon, and the two of them must have been close to Charle Frahma, Melbu Frahma's sister, as she still has fond memories of them as a couple and sees the way Dart resembles him when the group visits her.
Zieggy was the fiance of Rosie. They crossed both swords and love. Just looking at them made me feel embarrassed. Charle Frahma, Disc 4: Spring Breath Town Ulara
As Zieg coldly explains in a series of incredible revelations, time dissolved the spell that held him captive and forced him awake 11,000 years away from home. In a world that doesn't remember him, with everyone he once knew long dead, he continued living by building a new home, a family – until Neet was attacked by the Black Monster 18 years ago. Though he escaped the initial attack with his family, Zieg decided to walk back into the fire to call upon the Dragoon Spirit and save the home he has found. Rose and Dart believed him to be dead in different roles, yet now he stands in front of them as a stranger; though he clearly knows who they are, he is the enemy they must fight.
The conclusion of his story is told in a different part of this shrine, but a few last words concerning Rose and Zieg's present relationship: Is Rose's love for Zieg as strong as ever? I don't know, 11,000 years is a long time. She still thinks of him though, whether with affection or with regret. Has Zieg moved on? I think he had to, in order to stay alive in an unfamiliar age. But that doesn't have to mean that Rose isn't still in his heart (which in turn needn't mean that he cherished his new love, Dart's mother, less).
The game may not give clear answers to these questions, but it also doesn't have to – because the element that most likely drew them to each other an eternity ago and united them during the Dragon Campaign was their devotion and conviction, and, if nothing else, those values still live on in both of them: Rose continues to kill as the Black Monster, and though seeing Zieg alive leaves her shaken, her wish to protect the world never so much as wavers even if it means having to fight the man she once loved. As for Zieg...
What I found on the ground was only this. It's a memento, the only thing my father carried around all the time. Dart, Disc 1: Prairie
Zieg kept his Dragoon Spirit close by even if the days as a hero were long gone and the world had no need for Dragoons anymore – surely as something to remind him of who he once had been and of his dear comrades, but, as is later revealed, he also didn't hesitate to call upon it in order to protect the world and its people once more. In the end, both Zieg and Rose's loyalty to their vision have endured the test of time.